Fused loop of filamentous material and apparatus for making same

ABSTRACT

A fused loop of an elongated material, such as a surgical suture, and apparatus for making the loop. Portions of one or more segments to be joined together are fused in a welding process to form a welded joint. The shear area of the fused portion of the joint determines the strength of the joint and is thus preferably relatively large. Various configurations for the welding apparatus facilitate the creation of relatively large fused portions of the joint by maximizing contact between at least one of the welding members of the apparatus and at least one of the segments to be joined.

This application is a divisional of Ser. No. 08/919,297 filed Aug. 28,1997, now U.S. Pat. No. 5,893,880.

FIELD OF THE INVENTION

The invention relates to improvements in sutures and suturingtechniques, and more particularly to materials and devices for makinghigh-strength fused suture loops during surgical procedures.

BACKGROUND OF THE INVENTION

In surgical procedures, a monofilamentous suture is typically used tostitch or secure the edges of tissue together to maintain them inproximity until healing is substantially completed. The suture isgenerally directed through the portions of the tissue to be joined andformed into a single loop or stitch, which is then knotted or otherwisesecured in order to maintain the wound edges in the appropriaterelationship to each other for healing to occur. In this manner a seriesof stitches of substantially uniform tension can be made in tissue.Because the stitches are individual and separate, the removal of onestitch does not require removal of them all or cause the remainingstitches to loosen. However, each individual stitch requires anindividual knot or some other stitch-closing device for securing thestitch around the wound.

It is sometimes necessary or desirable to close a wound site withsutures without having to form knots or incorporate loop-closing devicesin the sutures, such as, for example, in surgical repair of delicateorgans or tissues, where the repair site is relatively small orrestricted. A fused suture loop must provide the appropriate tension onthe wound edges and the appropriate strength to maintain the wound edgesin sufficient proximity for a sufficient time to allow healing to occur.

Polymer sutures are particularly amenable to various fusing or joiningprocesses, such as, for example, welding, whereby sections of thesutures can be fused together upon application of sufficient heat to thesections to cause partial melting and fusion of the sections. Becausethe direct application of heat to sutures in situ may produceundesirable heating of the surrounding tissue, it is preferred to applynon-thermal energy to the suture material in situ to induce localizedheating of the suture material in the areas or sections to be fused. Inparticular, ultrasonic energy may be effectively applied to sections ofsuture materials to induce frictional heating of the sections in orderto fuse or weld them together.

While sutures typically fail under tensile loads applied along theprincipal axis of the suture, suture welds often fail in shear, i.e., inthe plane of the fused region between the overlapped segments of suturematerial. It is desirable to have the failure strength of the suturejoint be at least as great as the failure strength of the suturematerial away from the joint.

U.S. Pat. No. 5,417,700 to Egan and U.S. Pat. No. 3,515,848 to Winstonet al. disclose apparatus and methods for ultrasonic welding of sutures.The Winston et al. patent discloses, for example, the application ofmechanical energy to a segment of material to be joined in either of twodifferent directions. For joining plastic suture materials, mechanicalenergy is applied in a direction substantially parallel to the axes ofthe segments to be joined. For joining metallic suture materials,mechanical energy is applied in a direction substantially normal tothese axes. The Winston et al. patent further discloses the use of aspherical welding tip for use in joining metallic suture materials.

Although ultrasonic welding of sutures is known, it has heretofore beendifficult or impossible to control the suture welding process in orderto produce suture welds of sufficient strength and reliability toreplace, or enhance the strength of, suture knots or other loop closuredevices.

It is therefore an object of the present invention to overcome thedisadvantages inherent in prior art suture loop joints and joiningprocesses.

SUMMARY OF THE INVENTION

The present invention provides a fused loop of an elongated material,such as a polymeric or monofilamentous suture material, which has astrength in the joint region which is at least equal to, if not greaterthan, the strength of the parent material. The present invention alsoprovides means for controlling the size and shape of the fused portionof the joint region in order to maximize joint strength.

According to one aspect of the invention, there is provided a fused loopof an elongated material comprising one or more segments of the materialwhich extends along a principal axis. Portions of the segments arejoined together to form a loop at a joint region which extends betweenfirst and second ends. The joint region includes a first portion ofelongated material extending from the first end, a second portion ofelongated material extending from the second end, and a fused portion orlayer between and joining the first and second portions at pointsbetween the first and second ends of the joint region. The fused portionpreferably comprises a relatively thin layer of fused material from thefirst and second portions.

The term “fused”, as used herein, refers to material which has beenheated to a plastic or fluid state and subsequently allowed to cool, sothat the relatively highly-oriented molecular structure of the parentmaterial is transformed into a relatively randomly-oriented molecularstructure characterizing the fused portion of the joint region. The term“shear area”, as used herein, refers to the area of the fused portionbetween and substantially parallel to the segments of material joined inthe joint region. In contrast, the cross-sectional area of the segmentsor the fused portion refers to the area in a plane substantiallytransverse to the principal axes of the segments.

The elongated material in the first and second portions of the jointregion is characterized by a relatively high degree of molecularorientation in the direction of the principal axis of the material, andthus relatively high strength in the direction of the principal axis.The fused material in the fused portion of the joint region ischaracterized by a relatively random molecular orientation, and thusrelatively low strength in the direction of the principal axis of thematerial. The cross-sectional area of the first and second portions ofthe segment at the first and second ends of the joint region, yetoutside of (i.e., not abutting) the fused portion, is greater than thecross-sectional area of the first and second portions of the jointregion which abut the fused portion.

In one embodiment, the cross-sectional area of the first and secondportions of the segment at the first and second ends of the jointregion, yet outside of the fused portion, is approximately equal to thecross-sectional area of a segment of the elongated material outside ofthe joint region.

In a preferred embodiment, the total cross-sectional area of the firstand second portions of the joint region which abut the fused portion isa minimum at approximately the midpoint of the fused portion. In a morepreferred embodiment, the total cross-sectional area of the first andsecond portions of the segment at the midpoint of the fused portion isapproximately half the total cross-sectional area of the first andsecond portions at the first and second ends of the joint region andoutside of, or not abutting, the fused portion. In an especiallypreferred embodiment, the change in cross-sectional area of the firstand second portions of the segment, per unit length of those portions,is substantially constant over the length of the fused portion of thejoint region.

The elongated material may comprise a substantially monofilamentousmaterial, such as, for example, a polymer. In a preferred embodiment,the elongated material is a thermoplastic polymer, such as a surgicalsuture material.

The segments of elongated material are preferably joined in a weld atthe joint region. The weld can be effected with various types of energy,such as, for example, ultrasonic, laser, electrical arc discharge, andthermal energy.

The loop of elongated material can be made by joining portions of asingle segment of the elongated material. Alternatively, the loop can bemade by joining portions of multiple segments of the material.

The elongated material itself can comprise a single of a substantiallymonofilamentous material. Alternatively, the elongated material cancomprise multiple stands of a substantially monofilamentous materialwhich can be twisted, braided or otherwise interlinked.

Upon application of a tensile force to the joint region in the directionof the principal axis of the material, the first and second portions ofthe joint region are loaded substantially in tension, and the fusedportion of the joint region is loaded substantially in shear. In apreferred embodiment, the following equation,

A_(w)τ_(fw=A) _(u)σ_(fu),

is preferably substantially satisfied. A_(w) is the shear area of thefused portion, τ_(fw) is the shear stress to failure of the fusedportion, A_(u) is the total cross-section area of the first and secondportions near the first and second ends of the joint region and outsideof (not abutting) the fused portion, and σ_(fu) is the tensile stress tofailure of the first and second portions near the first and second endsand outside of (not abutting) the fused portion

According to another aspect of the invention, there is provide animprovement to ultrasonic welding apparatus. The apparatus typicallyincludes a first member having a first surface, a second member having asecond surface, and means for moving the first member relative to thesecond member to define a gap between them. The first acoustic couplingtherebetween and establish substantially continuous contact between thefirst surface and the segment over the length of the first surface.

In one embodiment, one of the first and second surfaces is substantiallyconvex and the other of the surfaces is substantially concave. Inanother embodiment, one of the first and second surfaces issubstantially convex or substantially concave, and the other of thesurfaces is substantially flat. In yet another embodiment, both of thefirst and second surfaces are substantially convex. In still anotherembodiment, both of the surfaces are substantially flat.

In another embodiment, the second member comprises a plurality ofcoupling portions which couple together to form the second surfaceduring a welding process and separate after completion of the weldingprocess to release the loop.

These and other features of the invention will be more fully appreciatedwith reference to the following detailed description which is to be readin conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by the following description andfigures, in which:

FIG. 1 is a perspective view of a fused loop of an elongated material;

FIG. 2A is an axial view of the fused loop of FIG. 1;

FIG. 2B is an axial view of several fused loops formed by joiningmultiple segments of material together;

FIG. 2C is a simplified perspective view of a multiple-stranded segmentof elongated material;

FIG. 3 is a cross-sectional view of the joint region of the fused loopof FIG. 2A, taken along, section lines A—A;

FIG. 4 is a cross-sectional view of the joint region of the fused loopof FIG. 2A, taken along section lines B—B;

FIG. 5 is a cross-sectional view of an end of the joint region of thefused loop of FIG. 2A, taken along section lines C—C;

FIG. 6 is a cross-sectional view of a segment of elongated material inthe fused loop of FIG. 2A, taken along section lines D—D;

FIG. 7A is a side elevational view of a joint region of a fused loopmade by ultrasonic welding;

FIG. 7B is a series of sectional views of a portion of the joint regionof the loop shown in FIG. 7A;

FIG. 8A is a side elevational view of a joint region of a different typeof fused loop made by laser welding or controlled coupling ultrasonicwelding;

FIG. 8B is a series of sectional views of a portion of the joint regionof the loop shown in FIG. 8A;

FIG. 9A is an axial view of a fused loop loaded in tension, in which thestrength of the joint region exceeds the tensile failure strength of theelongated material;

FIG. 9B is an axial view of a fused loop loaded in tension, in which thestrength of the joint region is less than the tensile failure strengthof the elongated material;

FIGS. 10A, 11A, 12A, 13A and 14A are exploded perspective views ofultrasonic welding members of various geometries, and segments ofmaterial to be welded in the gaps between their respective surfaces;

FIGS. 10B, 11B, 12B, 13B and 14B are exploded side elevational viewscorresponding to the views of FIGS. 10A, 11A, 12A, 13A and 14A;

FIGS. 15A, 16 and 17A are side elevational views of ultrasonic weldingmembers of various geometries engaged about a pair of segments ofmaterial to be welded;

FIG. 15B is a simplified side elevational view of the second weldingmember of FIG. 15A, uncoupled to show means for releasing the weldedloop from the welding apparatus;

FIG. 17B is a side elevational view of the second welding member of FIG.17A, uncoupled to show means for releasing the welded loop from thewelding apparatus;

FIG. 18 is an exploded perspective view of a segment of an elongatedmaterial with its ends aligned within an ultrasonic welding apparatusdesigned to produce a contoured lap weld;

FIG. 19A is an axial view of the segments of material within theultrasonic welding apparatus of FIG. 18, prior to welding; and

FIG. 19B is an axial view of the segments of material within theultrasonic welding apparatus of FIG. 18, immediately after the weldingprocess and prior to release of the loop.

Like elements in the respective FIGURES have the same reference numbers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a fused loop of an elongated material,such as a surgical suture. The loop has at least comparable strength toknotted loops or loops closed by other means by virtue of the propertiesof the fused portion of the joint region of the loop, as detailed morefully below.

As shown in FIG. 1, the fused loop 10 of the present invention comprisesone or more segments 12 of an elongated material, such as a surgicalsuture material or other substantially monofilamentous material, whichis amenable to bonding through the application of heat or energythereto. Suitable materials for the elongated material include polymers,especially thermoplastic materials such as, for example, nylon(polyamide), polypropylene, Dacron® (polyester), polyglycolic acid(PGA), polyglyconate, and polydioxanone.

The fused loop of the present invention is preferably formed through awelding process, in which segments of the material to be joined arelocally heated through the application of energy thereto until thesegments fuse together. Various types of welded joints can be formed bythe application of, for example, ultrasonic, thermal, laser, electricalarc discharge, or thermal energy to the segments, which can be joined,for example, in an overlapped joint.

FIG. 2A is an axial view of the fused loop shown in FIG. 1. The segment12 of elongated material extends along a principal axis X of thematerial, which can be straight or curved. One or more segments 12 ofthe material are typically formed into a loop by, for example,overlapping portions of the respective ends 12A, 12B of the segment, asshown in FIGS. 1 and 2A, to form a joint region 14. Alternatively, asshown in FIG. 2B, both terminal and nonterminal portions of the segmentsof the material can be overlapped to form several fused loops joined ina single joint region 14.

The segments may already be knotted in preparation for fusion bywelding, or they may simply be overlapped.

The elongated material can be made of a single strand of a substantiallymonofilamentous material, or it can comprise multiple strands, asindicated in FIG. 2C. The multi-stranded material can be twisted,braided or otherwise interlinked to increase the density, and thus thestrength, of the composite strand.

The joint region 14 extends between first and second ends 14A, 14B andincludes a first portion 16 of elongated material extending from thefirst end 14A, and a second portion 18 extending from the second end14B. The joint region 14 further includes a fused portion 20 which has asubstantially uniform thickness and which is disposed between the firstportion 16 and second portion 18 of the joint region. The fused portion20 is made of material from the first and second portions 16, 18 whichhas been fused together. In a preferred embodiment, all of the fusedmaterial is disposed within a fused layer or portion 20. However, someof the melted and fused material may form outside of the fused portion20 as a result of forces applied to the segments 16, 18 to compress themtogether during the welding process.

As mentioned previously, the elongated material of the type used insurgical sutures is substantially monofilamentous, and preferablypolymeric. Because the molecular structure of monofilamentous materialsis highly oriented along the principal axis of the material, thematerial exhibits relatively high strength in the direction of itsprincipal axis. The elongated material in the loop segment outside thejoint region 14, as well as in the first and second portions 16, 18 ofthe joint region, is characterized by a relatively high degree ofmolecular orientation in the direction of the principal axis X of thematerial. As a consequence of this highly oriented molecular structure,the strength of the elongated material outside the joint region, and inthe first and second portions 16, 18 of the joint region, is alsorelatively great in the direction of the principal axis X. On the otherhand, the material which makes up the fused portion 20 of the jointregion 14 is characterized by a relatively random molecular orientation,by virtue of its having been heated locally to a plastic state by theapplication of energy, such as ultrasonic energy, to the segmentportions 16, 18 which make up the joint region 14. As a consequence ofthis relatively nonoriented molecular structure, the strength of thematerial in the fused portion 20 of the joint region is relatively lowin the direction of the principal axis.

The shear area of the fused portion 20 is approximately defined as theproduct of the length L and the width W of the fused portion 20, asshown in FIG. 4. As will be detailed more fully below, for maximum jointstrength, it is desirable to have a relatively large shear area of thefused portion 20 of the joint region.

FIG. 6 indicates the cross-sectional area of a typical segment ofelongated material outside the joint region. Although the elongatedmaterial can be a strand or filament having a substantially circularcross-section, the invention is not limited to such geometries and caninclude elongated materials having eccentric or other cross-sectionalgeometries, such as, for example, relatively flat ribbons havingelliptical or rectangular cross-sections, or others. FIG. 5 indicatesthe cross-sectional area of the elongated material at the ends of thejoint region, outside of the fused portion 20. As can be seen in FIG. 3,7 and 8, the total cross-sectional area of the portions 16, 18 abuttingthe fused portion 20 of the joint region 14 is somewhat less than thetotal cross-sectional area of the first and second portions 16, 18 inthe joint region but outside of, and not abutting, the fused portion 20.As is clearly shown in FIGS. 2A and 3, some of the elongated material inportions 16 and 18 of the joint region is transformed during the weldingprocess from an elongated, relatively highly oriented material, to afused, relatively randomly-oriented material in the fused portion 20.Compression of the portions 16, 18 during the welding process ensuresthat the fused portion 20 has a relatively large shear area and arelatively small thickness.

The change in cross-sectional area of the overlapping segments 16, 18 inthe joint region is preferably uniform and gradual over the length ofthe fused portion 20. FIGS. 7A, 7B, 8A and 8B illustrate the change incross-sectional area of the overlapping segments of elongated materialin the joint region 14 throughout the length of the fused portion 20 fordifferent types of welded joints. At the ends 14A, 14B of the jointregion, outside of or beyond the fused portion 20, the cross-sectionalarea of the segment portions 16, 18 is a maximum value, as the segmentportions have not been caused to deform plastically at these points. Asthe cross-hatched areas 21 a-21 e in the joint region 14 indicate inFIG. 7B, the cross-sectional area of each of the overlapped segmentportions 16, 18 decreases gradually from a maximum value at the ends ofthe fused portion 20 to a minimum value at or near the midpoint of thefused portion. Preferably, at the midpoint of the fused portion 20, thetotal cross-sectional area of the segments 16, 18 not sacrificed to formthe fused portion is approximately half the total cross-sectional areaof the segments 16, 18 at the first and second ends 14A, 14B of thejoint region and beyond, or outside of, the fused portion 20.

The lap welded joint shown in FIG. 8A is characterized by a continuouslyvarying cross-sectional area of the segments 16 and 18 in the region ofthe fused portion 20. As indicated in FIG. 8B, the cross-sectional area21 a-21 e of one segment 16 continuously decreases from a maximum valueat end 14B to a minimum value at the opposite end 14A, whereas thecross-sectional area of the other segment 18 continuously increases froma minimum value at end 14B to a maximum value at the opposite end 14A.At approximately the midpoint of the fused portion 20, thecross-sectional areas of the segment portions 16, 18 are approximatelyequal and are preferably equal to about half the total cross-sectionalareas of the segment portions 16, 18 at the first and second ends 14A,14B of the joint region and outside the fused portion 20.

Other geometries of the first and second portions 16, 18 in the jointregion 14 which provide a uniform change in cross-sectional area of thejoined segments in the joint region are also considered to be within thescope of the invention.

In a preferred embodiment of the invention, the shear area of the fusedportion 20 of the joint region is sufficiently large to ensure that thejoint will not fail prematurely, i.e., before the parent elongatedmaterial fails. The joint preferably has a failure strength ofapproximately the strength of the parent material. Most preferably, thejoint has a failure strength in shear which is approximately equal tothe failure strength in tension of the parent material.

Upon application of a tensile force to the joint region 14 in thedirection of the principal axis X of the material, the first and secondportions 16, 18 of the joint region are loaded substantially in tensionand the fused portion 20 of the joint region is loaded substantially inshear. In this situation, the following equation,

A_(w)τ_(fw)=A_(u)σ_(fu),

is substantially satisfied, wherein A_(w) is the shear area of the fusedportion 20 (i.e., the area of the layer of the fused portion which isbetween the first and second portions 16, 18, not the cross-sectionalarea of this layer), τ_(fw) is the shear stress to failure of the fusedportion, A_(u) is the total cross-sectional area of the first and secondportions 16, 18 near the first and second ends of the joint region 14,outside of and not abutting the fused portion, and σ_(fu) is the tensilestress to failure of the first and second portions near the first andsecond ends, outside of and not abutting the fused portion.

If the above equation is not satisfied, the strength of the fusedportion 20 may be either stronger or weaker than the strength of theparent elongated material. It is of course preferred that the fusedportion 20 be at least as strong as the unfused parent material. If itis stronger, when the joint is loaded in tension, as indicated by forcearrows F in FIGS. 9A and 9B, the material will fail in tensile mode, andthe loop will break at a point which is outside the fused portion, andpossibly outside the joint region, as indicated in FIG. 9A. If the fusedportion 20 is weaker than the parent material, the fused material withinthe joint will fail in shear mode, and the loop will separate at thefused portion, as indicated in FIG. 9B.

FIGS. 10A-14B illustrate various geometries for ultrasonic weldingapparatus, and more particularly for the vibratory and stationarymembers of an ultrasonic welding-tip, which includes a first member 30and a second member 32. The first member 30 is capable of vibrating anddelivering mechanical energy at ultrasonic frequencies, as is known inthe art. The first member 30 is movable relative to the second member32, so that a gap or space can be defined between the first and secondmembers. The gap is sufficiently large to accommodate two or moresegments 16, 18 of material to be joined together. The ultrasonicwelding apparatus further includes fixture means for aligning andmaintaining the segments 16, 18 in a predetermined alignment andorientation during the welding process.

The first and second members 30, 32 each have respective surfaces 30A,32A which are contoured to promote acoustic coupling between the firstmember 30 and the segment 16 of material to be joined, and to providesubstantially continuous contact between at least the first surface 30Aand at least one of the segments to be welded. The size of the sheararea of the fused portion 20, and thus the strength of the joint region,is determined by the length and width of the surfaces 30A, 32A, theextent of contact between these surfaces and the segments 16, 18, andparticularly between the first surface 30A and the segment 16 closest tothe first surface, and the pressure exerted on the segments by the firstmember 30 in the direction of arrow 35 during welding.

In addition to the geometries of the surfaces of the first and secondmembers, the geometry of the material to be joined must be considered.Fused portions having the largest shear areas and the greatest jointstrengths can be obtained by configuring the surface 30A of the firstmember 30 to have a contour which corresponds to the contour of thematerial to be joined so as to ensure maximum contact with the segmentportion 16. For example, if the material is a filament having asubstantially circular cross-section, the surface 30A should have arounded contour to match the contour of the filament in contact with it.If the material is a substantially flat ribbon, the surface 30A shouldbe substantially flat to ensure maximum contact with the segment. If thematerial has a polygonal or elliptical cross-section, the contour of thesurface 30A should be grooved or channeled or otherwise shaped tocorrespond as closely as possible to the geometry of the cross-sectionof the material.

It is generally preferred to configure the ultrasonic welding tipmembers 30, 32 so that their respective surfaces 30A, 32A engage thesegment portions 16, 18 so as to provide a maximum shear area for thefused portion 20. Various geometries for the surfaces 30A, 32A areillustrated in FIGS. 10A-14B.

As shown in FIGS. 10A and 10B, the surface 30A of the first member 30 isconcave about the z and x axes, whereas the surface 32A of the secondmember 32 is convex about the z axis. The illustrated segments 16, 18have a circular cross-section but need not be limited to a particulargeometry. Contact between the first surface 30A and the top segment 16is substantially continuous over the entire length and width of thesurface 30A as a result of the contour of that surface. The shear areaof the resulting fused portion 20 is relatively large, and thus thestrength of the fused portion can be expected to be relatively high.

An advantage of incorporating a convex curvature to the second surface32A is that the length of the joint region 14 in the direction of theprincipal axis of the material can be reduced, thereby decreasing thediameter of the resulting fused loop of suture material.

The surfaces 30A, 32A of the embodiment illustrated in FIGS. 14A and 14Bhave the same relationship to each other as in the embodiment of FIGS.10A and 10B. The resulting fused portion 20 is relatively large, withrelatively high strength.

As shown in FIGS. 15A, 16 and 17A, the first surface 30A of the firstmember 30 can have a channeled or grooved geometry to increase theextent of contact between the first surface 30A and the segment 16. Asalso indicated in FIGS. 15B, 16 and 17B, the second member 32 may becomprised of multiple parts which act to confine and maintain thealignment of the segments 16, 18 during the welding process. Thecoupling portions of the second member separate after the weldingprocess to release the joined material from the confines of the weldingapparatus without requiring the loop to be moved or otherwisemanipulated. FIGS. 15A, 15B and 16A illustrate one type of ultrasonicwelding apparatus, in which the second member 32 couples togetherbeneath the segments of material joined at the joint region. The coupledmembers remain engaged during the welding process, as shown in FIGS. 15Aand 16A, and separate after the welding process by a hinging or pivotingaction to release the loop, as shown in FIG. 15B.

FIGS. 17A and 17B illustrate another type of apparatus, in which themultiple parts of the second member 32 slide away from each other torelease the joined loop. Other configurations for the second member 32which permit the loop to be released after the welding operation iscompleted are considered to be within the scope of the invention.

FIGS. 18, 19A and 19B illustrate still another configuration for thewelding apparatus, in which the segment portions 16, 18 to be welded areconfined and aligned or oriented relative to each other within the wallsof the second member 32. This apparatus produces welded joints having afused portion 20 in a vertical orientation instead of a horizontalorientation. In this apparatus, the first member 30 is complementarywith and fits inside two sections of the second member 32, which extendvertically on either side of the first member. The surfaces 30A, 32A ofthe first and second members are substantially flat, although they canbe cambered and contoured otherwise, as previously discussed. As shownin FIG. 19A, the overlapping portions 16, 18 of segment 12 of materialto be joined together are oriented in a vertically diagonal alignmentwithin the multiple parts of the second member 32. During the weldingprocess ultrasonic energy is delivered from a power supply and convertedto mechanical energy to establish local frictional heating between thesegment portions 16, 18. Pressure is exerted on the segment portions 16,18 in the direction of arrow 35 as the segments are heated to a plasticstate, causing portions of the segments to flow and to fuse in avertically oriented fused portion 20. Because the first and secondmembers 30, 32 are configured to confine and maintain the alignment ofthe overlapping segments during the welding process, the joint region 14and fused portion 20 are relatively dense and compact, with little, ifany, fused material disposed in regions outside of the fused portion 20.It is desirable to minimize the extrusion of fused material beyond thefused portion 20 so as to maximize the strength of the loop joint regionand to avoid irritation of the surrounding tissue.

As in the above embodiments, the coupling portions of the second member32 can be separated after the welding process to release the joinedloop.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription. All changes that come within the meaning and range of theequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. An ultrasonic suture welding apparatus comprisinga first member extending along a first (Y) axis and having a firstsurface at an end thereof, said first member being capable of vibratingand delivering mechanical energy at ultrasonic frequencies to said firstsurface, a second member having a second surface, means for moving saidfirst member relative to said second member to define a gap between saidfirst surface and said second surface, wherein said second member isstationary relative to said first member, and fixture means adapted toreceive and maintain adjacent two or more segments of a suture materialto be welded together in a predetermined alignment at least in part inthe direction of a second (X) axis in said gap between said first andsecond surfaces of the first and second members during a weldingoperation, where said Y axis is perpendicular to said X axis: wherein acontour of at least said first surface substantially is concave withrespect to said X axis, and corresponds to the contour of a segment ofsaid suture material to be welded, so as to promote acoustic couplingtherebetween and establish substantially continuous contact between saidfirst surface and said segment over the length of said first surface. 2.Ultrasonic welding apparatus according to claim 1, wherein at least oneof said first and second surface is substantially convex with respect toa third (Z) axis, and the other of said surfaces is substantiallyconcave with respect to said Z axis, wherein said Z axis isperpendicular to said X and Y axes.
 3. Ultrasonic welding apparatusaccording to claim 1, wherein at least one of said first and secondsurfaces is substantially convex or substantially concave with respectto a third (Z) axis, and the other of said surfaces is substantiallyflat with respect to said Z axis, wherein said Z axis is perpendicularto said X and Y axes.
 4. Ultrasonic welding apparatus according to claim1, wherein both of said first and second surfaces are substantiallyconvex with respect to a third (Z) axis, wherein said Z axis isperpendicular to said X and Y axes.
 5. Ultrasonic welding apparatusaccording to claim 1, wherein both of said first and second surfaces aresubstantially flat with respect to a third (Z) axis, wherein said Z axisis perpendicular to said X and Y axes.
 6. Ultrasonic welding apparatusaccording to claim 1, wherein said second member comprises a pluralityof coupling portions which couple together to form said second surfaceduring a welding process and separate to release said loop after saidwelding process is completed.